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Pressure Switch Thread Sealant


oggie

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Hi some time ago I had to have the oil pressure switch replaced on my Isuzu engine because a ham fisted service person damaged the original and didn't bother to tell me about it.

When the switch was replaced by a competant mechanic it was the devils own to get a good seal, but after a couple of ettempts was managed.

Now some 15 months later it has started weeping a small amount of oil again so I was going to remove it and try yet again to seal it.

What would you recomend to get a good oil pressure seal? I was thinking of using PTFE but although this is great for plumbing I am not so sure about using it on an engine. The other option is Loctite thread sealant but there are so many of them I wouldn't know which one to use bearing in mind it has to withstand the oil pressure and the heat from the engine.

Any thoughts would be appreciated.

 

Oggie

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An oil pressure switch should seal in one of two ways. Either by compressing a copper washer, or with a tapered thread. Sounds to me like you have a mis-match.

 

 

Hope not was supplied by HMI and fitted by one of their warranty repair men.

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An oil pressure switch should seal in one of two ways. Either by compressing a copper washer, or with a tapered thread. Sounds to me like you have a mis-match.

Hi

If the top of the thread has not got a machined face (a spot face),on the block, a washer will not seal it.

Has the switch got a shoulder underneath the tightening hexagon? again a washer will not seal it.

PTFE should seal it, if the B.S.P. male thread is tapered and the port in the block is parallel and is deep enough to allow the pressure switch not to bottom out.

Loctite should be used with caution as it can proove impossible to undo without damage if the wrong grade is used. You should always be able to undo or tighten the PTFE joint.

Another possibility is it the thread that's leaking or the switch itself?

Best of luck, Peter

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Hi

If the top of the thread has not got a machined face (a spot face),on the block, a washer will not seal it.

Has the switch got a shoulder underneath the tightening hexagon? again a washer will not seal it.

PTFE should seal it, if the B.S.P. male thread is tapered and the port in the block is parallel and is deep enough to allow the pressure switch not to bottom out.

Loctite should be used with caution as it can proove impossible to undo without damage if the wrong grade is used. You should always be able to undo or tighten the PTFE joint.

Another possibility is it the thread that's leaking or the switch itself?

Best of luck, Peter

 

Peter,

thankyou for your advice, I have spent the last few days onboard giving everything a good service and I got to have a good look at the problem.

 

There is a brass nut shaped fitment screwed into the engine block with a copper washer to seal it. Within this brass fitment is a threaded hole for the actual pressure switch to screw into, its from this thread that the oil is leaking.

I took the pressure switch out and wrapped a couple of turns of PTFE around it and screwed it back, but I think it is still leaking.

I now suspect that when the ham fisted mechanic damaged it originally he has opened the brass thread causing it to leak, so I will be contacting Isuzi to see if the said brass fitment can be purchased and replaced, hopefully solving my problem.

Thanks again for your advice,

 

Bob.

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You might, (or might not) be surprised just how quickly any threaded brass items can develop a hairline crack - often nigh on invisible to the eye.

 

A standard threaded part that was used in the water supply to our cassette loo failed unexpectedly twice, (not after frost), and although you could barely see a split, water was pi**ing out. (I have since replaced with a completely different solution).

 

I would have thought that with use of brass in the way you describe damage may extend to more than the threads, particularly if over-tightening has been used as an attempted solution to a leak.

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Peter,

thankyou for your advice, I have spent the last few days onboard giving everything a good service and I got to have a good look at the problem.

 

There is a brass nut shaped fitment screwed into the engine block with a copper washer to seal it. Within this brass fitment is a threaded hole for the actual pressure switch to screw into, its from this thread that the oil is leaking.

I took the pressure switch out and wrapped a couple of turns of PTFE around it and screwed it back, but I think it is still leaking.

I now suspect that when the ham fisted mechanic damaged it originally he has opened the brass thread causing it to leak, so I will be contacting Isuzi to see if the said brass fitment can be purchased and replaced, hopefully solving my problem.

Thanks again for your advice,

 

Bob.

Bob,

You may get a adapter the "brass nut shaped fitment" if I've read you right, from a plumbers merchants, take the old one with you as a sample.

The way you wind the PTFE onto the switch is important, you want the tape to be wound into the threads as you tighten the switch,not wiped out of them.

Tightly wind enough on so that you can just see the threads shape showing through the tape, two turns is probably not enough,as long as you can start the switch threads, it should be OK.

Sorry if this is teaching Grandma to suck eggs :lol:

I suppose the adapter bush may be split or the thread partially stripped by the tapered male thread on the switch (if this is the case)? and as the previous attempts have all failed then the bush seems to be favourite for renewal.

If you can easilly undo the adapter, you could as a last resort use a semi-permanent thread sealant as you can always undo the whole thing and replace both if you have to, and check the depth of the threaded portions while you have it out to hand so that you know for sure that one is not bottoming out on the other before the thread is tight.

Good luck, let us know how you get on.

Peter

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Hi some time ago I had to have the oil pressure switch replaced on my Isuzu engine because a ham fisted service person damaged the original and didn't bother to tell me about it.

When the switch was replaced by a competant mechanic it was the devils own to get a good seal, but after a couple of ettempts was managed.

Now some 15 months later it has started weeping a small amount of oil again so I was going to remove it and try yet again to seal it.

What would you recomend to get a good oil pressure seal? I was thinking of using PTFE but although this is great for plumbing I am not so sure about using it on an engine. The other option is Loctite thread sealant but there are so many of them I wouldn't know which one to use bearing in mind it has to withstand the oil pressure and the heat from the engine.

Any thoughts would be appreciated.

 

Oggie

 

You could try Loctite 55 thread sealing cord, I prefer it to PTFE tape tho prob not quite as good on small/fine threads.

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You could try Loctite 55 thread sealing cord, I prefer it to PTFE tape tho prob not quite as good on small/fine threads.

Bit concerned about advice for using Loctite 55 cord.

Definately not to be recommended for small fine brass threads,more suitable for malleable iron.

Manufacturer instructions advise roughing up the threads to give the cord some grip I suppose, using gland pliers :lol:

If a thread has been produced to give a good fit and therefore seal properly then to mash it up will not be very good for a brass on brass type assembly.

Loctite products are expensive and good used properly but usually have a shelf life, PTFE is cheaper and lasts indefinately in the tool box,and the joint is usually able to be undone without damage.

Regards Peter

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PTFE not recomended on any oil product, it will soften up and decay after a while.

 

I use Loctite 577 ideal for small brass threads, fills damaged threads and is removable.

 

Good for 3000psi

 

Andrew

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PTFE not recomended on any oil product, it will soften up and decay after a while.

 

I use Loctite 577 ideal for small brass threads, fills damaged threads and is removable.

 

Good for 3000psi

 

Andrew

I am prepared to prooven wrong but I think the only reason that PTFE is not used on hydraulics is because new soft loose strands of the tape may cause valve assemblies to jam, not because it affects the tape, its impermeable.

On the return filtered side of a circuit or a non flow or slow moving condition like a pressure switch in a Internal combustion engine it's OK I think.

I've personally undone many externally dry PTFE joints after many years of service and have not noticed any "decay".

 

Loctite 577 is for Stainless, I believe and "cures" (goes off)in the joint.

If the Brass tapered BSP thread is tightened with the cured 577 in the threads, wouldn't the undoing process increase the chances of stripping the thread or round off the hexagon? (Steel being stronger than Brass).

PTFE is brilliant as a friction reducer and will always undo.

I would rather occasionally attend to a minor weep than have to heat up to 250 degrees C or drill out the fitting/switch to remove it. :lol:

3000 psi depends on the joint gap,hope my oil never gets to that, there wouldn't half be a mess :lol:

 

No I do not have any connection with PTFE or a tape company i just think that a roll of PTFE is more useful on the canal side than a fancy bottle of chemical gunge, that has a shelf life, takes time to cure, needs controlled storage temperatures, is probably expensive and might cause problems later on.

 

The blue stuff is Hylomar a gasket jointing compound.

 

I do hope this helps.

 

Peter

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I am prepared to prooven wrong but I think the only reason that PTFE is not used on hydraulics is because new soft loose strands of the tape may cause valve assemblies to jam, not because it affects the tape, its impermeable.

On the return filtered side of a circuit or a non flow or slow moving condition like a pressure switch in a Internal combustion engine it's OK I think.

I've personally undone many externally dry PTFE joints after many years of service and have not noticed any "decay".

 

Loctite 577 is for Stainless, I believe and "cures" (goes off)in the joint.

If the Brass tapered BSP thread is tightened with the cured 577 in the threads, wouldn't the undoing process increase the chances of stripping the thread or round off the hexagon? (Steel being stronger than Brass).

PTFE is brilliant as a friction reducer and will always undo.

I would rather occasionally attend to a minor weep than have to heat up to 250 degrees C or drill out the fitting/switch to remove it. :lol:

3000 psi depends on the joint gap,hope my oil never gets to that, there wouldn't half be a mess :lol:

 

No I do not have any connection with PTFE or a tape company i just think that a roll of PTFE is more useful on the canal side than a fancy bottle of chemical gunge, that has a shelf life, takes time to cure, needs controlled storage temperatures, is probably expensive and might cause problems later on.

 

The blue stuff is Hylomar a gasket jointing compound.

 

I do hope this helps.

 

Peter

 

Obviously never used it then, never mind, you keep tending your minor weeps and I'll keep my 577 in my tool box.

 

Ho! the blue stuff could be loctite 243, but I wouldn't use that.

 

Andrew

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Obviously never used it then, never mind, you keep tending your minor weeps and I'll keep my 577 in my tool box.

 

Ho! the blue stuff could be loctite 243, but I wouldn't use that.

 

Andrew

 

No never used it, never needed too, just trying to help out a guy with a leak :lol:

 

Peter

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No never used it, never needed too, just trying to help out a guy with a leak :lol:

 

Peter

 

Well Andrew if you want to help, what's the use in advocating a product that "when stored below 8 degrees C and above 28 degrees C can adversely affect product properties"?

"Optimal storage being 8 degrees C to 21 degrees C."

How the chuffin heck do we do that in a Canal Boat?even if we could afford £16 for a small bottle is this product really suitable?

Do you have a temperature controlled tool box? Have you ever undone any of the fine threaded brass joints you have made?

Loctite 577 is'n't for fine threads anyway.The object is to assist Bob with his problem not give him some more!

I,m done with this, I would like to wish the guy who has to work on any brass parts in your engine in future the very best of luck.

 

Peter

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PTFE not recomended on any oil product, it will soften up and decay after a while.

 

I use Loctite 577 ideal for small brass threads, fills damaged threads and is removable.

 

Good for 3000psi

 

Andrew

Surely it wouldn't be much good for non-stick frying pans if oil did soften and decay it? :lol:

 

cheers,

Pete.

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Well Andrew if you want to help, what's the use in advocating a product that "when stored below 8 degrees C and above 28 degrees C can adversely affect product properties"?

"Optimal storage being 8 degrees C to 21 degrees C."

How the chuffin heck do we do that in a Canal Boat?even if we could afford £16 for a small bottle is this product really suitable?

Do you have a temperature controlled tool box? Have you ever undone any of the fine threaded brass joints you have made?

Loctite 577 is'n't for fine threads anyway.The object is to assist Bob with his problem not give him some more!

I,m done with this, I would like to wish the guy who has to work on any brass parts in your engine in future the very best of luck.

 

Peter

 

Well, it so happens I've just got back from a call out to a damaged lubrication system with 1/8 bspt brass fittings, been in about 5 years.

 

So the answer is, yes!

 

Over the passed 15 years or so I've used various sealants and this comes out best every time.

 

Don't knock it if you haven't used it.

 

Andrew

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Well, it so happens I've just got back from a call out to a damaged lubrication system with 1/8 bspt brass fittings, been in about 5 years.

 

So the answer is, yes!

 

Over the passed 15 years or so I've used various sealants and this comes out best every time.

 

Don't knock it if you haven't used it.

 

Andrew

Well Done, how convenient :lol:

You didn't say what bother you had though!

 

You only managed to answer one question from previous post?

 

Over the past 40 years i have had to deal with many examples of incorrect use of chemical thread sealants, most were hard work and expensive to correct often resulting in new parts being required and down time on a variety of machine tools.

 

Why would i want to use it? I don't have any medium sized stainless pipe threads that need sealing on my boat or engine that require a medium strength loctite,(This from Loctites Data sheet).

I would prefer to use the manufacturers recommended for a fine thread thanks,(542 is it)? if I ever feel the need to risk it that is.

 

Be Lucky(seems like you have been so far) :lol:

 

Peter

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Well Done, how convenient :lol:

You didn't say what bother you had though!

 

You only managed to answer one question from previous post?

 

Over the past 40 years i have had to deal with many examples of incorrect use of chemical thread sealants, most were hard work and expensive to correct often resulting in new parts being required and down time on a variety of machine tools.

 

Why would i want to use it? I don't have any medium sized stainless pipe threads that need sealing on my boat or engine that require a medium strength loctite,(This from Loctites Data sheet).

I would prefer to use the manufacturers recommended for a fine thread thanks,(542 is it)? if I ever feel the need to risk it that is.

 

Be Lucky(seems like you have been so far) :lol:

 

Peter

 

What is your gripe, I've used something that works. So you've been doing it 4 years longer than me and I too have come across wrong applications of sealant, like PTFE.

It says it can be used on stainless steel threads without any other preperation not only on stainless steel. In my catalogue it states use on Copper, Brass, Cast iron, Stainless steel and Galvanised.

I too would use 542 if I use hydraulic taper to taper threads but, I don't.

Sorry, not luck, practical experence, 36 years of fixing other peoples leaks.

 

Andrew

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What is your gripe, I've used something that works. So you've been doing it 4 years longer than me and I too have come across wrong applications of sealant, like PTFE.

It says it can be used on stainless steel threads without any other preperation not only on stainless steel. In my catalogue it states use on Copper, Brass, Cast iron, Stainless steel and Galvanised.

I too would use 542 if I use hydraulic taper to taper threads but, I don't.

Sorry, not luck, practical experence, 36 years of fixing other peoples leaks.

 

Andrew

 

I'll try and be Doveish here seeing as how a forum storm seems to be brewing. :lol:

 

What did the old boys use before ptfe and loctite were invented? String and grease? :lol:

 

Graham R.

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